Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$14.30	8.124%	$15.4617	$15.46	$15.45	$15.50
Purchase #2	$175.64	7.316%	$188.4898	$188.49	$188.50	$188.50
Purchase #3	$70.55	11.848%	$78.9088	$78.91	$78.90	$78.90
Purchase #4	$181.74	12.512%	$204.4793	$204.48	$204.50	$204.50
Purchase #5	$239.51	8.467%	$259.7893	$259.79	$259.80	$259.80
Purchase #6	$107.42	9.658%	$117.7946	$117.79	$117.80	$117.80
Purchase #7	$237.55	8.811%	$258.4805	$258.48	$258.50	$258.50
7 purchase totals =	$1,026.71		$1,123.4040	$1,123.40	$1,123.45	$1,123.50